U.S. patent number 4,078,910 [Application Number 05/676,731] was granted by the patent office on 1978-03-14 for glass sleeve fiber joining.
This patent grant is currently assigned to International Standard Electric Corporation. Invention is credited to David George Dalgoutte.
United States Patent |
4,078,910 |
Dalgoutte |
March 14, 1978 |
Glass sleeve fiber joining
Abstract
A permanent butt joint between optical fibers is made by
inserting the bare fiber ends into the opposite ends of a slightly
oversized bore in a sleeve of glass of lower melting point than the
fibers. The central region of the sleeve is collapsed by softening.
By this collapse, the butted fibers are brought into alignment. The
joint may be protected with a length of heat shrink tubing fitted
over the sleeve.
Inventors: |
Dalgoutte; David George
(Harlow, EN) |
Assignee: |
International Standard Electric
Corporation (New York, NY)
|
Family
ID: |
10148386 |
Appl.
No.: |
05/676,731 |
Filed: |
April 14, 1976 |
Foreign Application Priority Data
|
|
|
|
|
May 15, 1975 [UK] |
|
|
20587/75 |
|
Current U.S.
Class: |
65/407; 385/98;
392/407; 65/36; 65/432; 65/54 |
Current CPC
Class: |
C03C
27/06 (20130101); G02B 6/255 (20130101); G02B
6/2558 (20130101); G02B 6/3835 (20130101); G02B
6/3861 (20130101) |
Current International
Class: |
C03C
27/06 (20060101); G02B 6/38 (20060101); C03C
025/02 (); C03C 023/20 () |
Field of
Search: |
;65/DIG.7,4B,4A,4R,3A,3C,36,54 ;350/96C |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fisher; Richard V.
Assistant Examiner: Miga; Frank W.
Attorney, Agent or Firm: Peterson; Thomas L.
Claims
What is claimed is:
1. A method of joining glass optical fibers comprising the steps
of:
introducing two bare sections of optical fibers, each having a flat
end substantially normal to the fiber axis, into opposite ends of a
glass sleeve having a lower melting point than that of the fibers,
which sleeve has a bore providing a clearance fit over the bare
fibers;
butting the two flat ends together within the sleeve; and
heating the sleeve in the vicinity of the fiber ends while the
sleeve and filter ends are unstressed to a temperature to cause the
sleeve to collapse onto the fibers, the said heating step raising
the temperature of the fibers to a point below the melting point
thereof, whereby a joint is formed while the fiber ends are not
distorted.
2. A method of joining glass fibers as set forth in claim 1
wherein:
a fillet of adhesive is applied to each end of the sleeve after the
step of heating the sleeve in the vicinity of the fiber ends.
3. A method of joining glass fibers as set forth in claim 1
wherein:
after the joint is made a length of heat-shrinkable plastic tubing
is positioned around the sleeve with its ends extending beyond both
ends of the sleeve and the tubing is heated to cause it to shrink
onto the sleeve and the adjoining emergent regions of fiber.
4. A method of joining optical fibers as set forth in claim 1
wherein:
the fibers are plastic coated whose ends are stripped of their
sheathing prior to their insertion into the sleeve.
5. A method of joining optical fibers as set forth in claim 1
wherein:
the fibers are made of silica.
6. A method of joining optical fibers as set forth in claim 5
wherein:
the sleeve is made of boro-silicate or soda-lime glass.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method of joining glass optical
fibers.
The need for forming butt joints or splices for optical fibers in
the field of fiber optics communications is well known. Reference
is made to U.S. Pat. Nos. 3,768,146 and 3,810,802 for examples of
single fiber joints. The purpose of the present invention is to
provide a simple and inexpensive method of making an optical fiber
joint.
SUMMARY OF THE INVENTION
According to the principal aspect of the present invention, there
is provided a method of joining glass optical fibers which method
includes the step of introducing two bare sections of optical
fibers, each havng a flat end substantially normal to the fiber
axis, into opposite ends of a glass sleeve having a lower melting
point than that of the fibers. The sleeve has a bore that provides
a clearance fit over the bare fibers. The two ends of the fibers
are butted together within the sleeve. The sleeve is heated in the
vicinity of the fiber ends so as to cause the sleeve to collapse
onto the fibers.
In the case of plastic coated fibers, the coatings are stripped to
expose the bare fibers before the ends are inserted into the
sleeve. A length of heat-shrinkable plastic tubing slightly longer
than that of the sleeve may be slipped over one fiber prior to
insertion into the sleeve. Then, after the glass sleeve has been
collapsed onto the fiber ends, the heat-shrinkable plastic tubing
is slid over the sleeve and shrunk over its end to give a measure
of mechanical strengthening at the region when the fibers emerge
from the glass sleeve.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1, 2, and 3 are longitudinal sectional views illustrating
successive stages in the manufacture of an optical fiber joint
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A length of plastic coating is stripped from the ends of two
plastic clad glass optical fibers 1 and 2, typically 1 mm in
diameter, to expose regions 3 and 4 of bare fiber, typically
70-100.mu.m in diameter. The manner of stripping will depend upon
the particular plastic material used for the coating. With a
polypropylene coating the use of hot xylene as a solvent presents
some difficulties, and so melting off the coating with a hot wire,
a hot air gun, or soldering iron is preferred. If desired, the
bared fiber can be immersed in cold xylene in case traces of the
coating have been left, but these will dissolve only comparatively
slowly in the cold solvent. One of the difficulties in using hot
xylene is that the stripping is not confined to the immersed
portion of the coating because the vapor is also reactive.
The two bared regions 3 and 4 of fibers are provided with flat end
faces 5 and 6 by any suitable technique. A preferred technique is
to score lightly the fiber surface and then subject the fiber to
tensile stress until it breaks. Another technique involves placing
the fiber on a sharp edge, such as that of a razor blade, applying
the spark of a tesla coil to the fiber at the sharp edge, and then
breaking the fiber at this point by bending it or applying
tension.
The two prepared ends of the fibers are next introduced into
opposite ends of a glass sleeve 7, as seen in FIG. 1, and butted
together somewhere near its midpoint, as seen in FIG. 2. Prior to
this, a length of heat shrinkable plastic tubing 8 may be slipped
over one fiber. This tubing is an optional item which may be used
to given mechanical protection to the finished joint, particularly
at the regions where the two fibers emerge from the glass sleeve.
The sleeve is typically between 1/2 cm and 1 cm in length, and the
heat shrinkable tubing 7 typically about 1 cm longer than the
sleeve, so that after the joint has been made and the tubing
slipped over the sleeve it will extend a short distance beyond each
end of the sleeve.
The bore of the sleeve does not have to be a tight fit over the
bare fibers, but is a clearance fit that is large enough for the
fiber ends to be readily inserted by hand. To this end, it is
convenient to employ sleeving that has a larger bore than is
required, to soften a short length, and to draw it out or partially
collapse it forming a necked portion of appropriate size, not
shown. The central region of this necked portion is then parted
from the remainder to provide a sleeve with slightly flared ends.
If a sleeve is cut from parallel-walled sleeving having a bore of
the appropriate size, the bore may be slightly flared at both ends
by enlarging the ends with the tip of a heated needle. Such flaring
is, however, not essential.
The central region of the glass sleeve is placed in a loop 9 of
electrical resistance heating wire which is energized to raise the
temperature and to soften the central region 10 of the sleeve which
collapses around the fiber ends while the sleeve and fiber ends are
unstressed and bringing them into alignment. It is believed that
this collapse results primarily from the effects of surface
tension. It is not desired that the fiber ends shall melt during
this collapsing process, and, therefore, the material of the sleeve
is chosen which has a lower melting point than that of the fibers.
In the case of silica fibers, the sleeve may be made of a
conventional boro-silicate or soda-lime glass. The thermal
expansion mismatch between silica and such glasses is liable to
produce a certain amount of strain where the two glasses are sealed
together. Where, for mechanical or optical reasons, this strain is
too large to be acceptable for particular applications, a high
silica (c. 96% SiO.sub.2) glass may be used for the sleeve, such as
that manufactured under the trademark VYCOR. Alternatively, the
strain may be reduced by choosing a glass with a low melting point,
such as one of the lead glasses.
Optionally, each fiber may be further secured in the sleeve by the
application of a fillet 11 of quick-setting cement, such as
cycloacrylate adhesive, around the point of its emergence from the
sleeve, as seen in FIG. 3. Finally, the length of heat-shrinkable
tubing 7 is slipped over the sleeve 6 and is heated with a hot air
gun to shrink it down onto the sleeve and the portions of the fiber
adjacent the sleeve ends.
The dimensions of the sleeve 7 and optical fibers disclosed herein
are given by way of example only, and not by limitation. Further,
fibers other than plastic coated glass fibers could be used in the
present invention.
* * * * *